7.2 I2C-bus serial interface

 

The LM75B can be connected to a compatible 2-wire serial interface I2C-bus as a

slave device under the control of a controller or master device, using two device terminals,

SCL and SDA. The controller must provide the SCL clock signal and write/read data

to/from the device through the SDA terminal. Notice that if the I2C-bus common pull-up

resistors have not been installed as required for I2C-bus, then an external pull-up resistor,

about 10 k

, is needed for each of these two terminals. The bus communication protocols

are described in Section 7.10.

 

7.2.1 Bus fault time-out

 

If the SDA line is held LOW for longer than tto (75 ms minimum / 13.3 Hz; guaranteed at

50 ms minimum / 20 Hz), the LM75B will reset to the idle state (SDA released) and wait

for a new START condition. This ensures that the LM75B will never hang up the

bus should there be conflict in the transmission sequence.

 

7.3 Slave address

 

The LM75B slave address on the I2C-bus is partially defined by the logic applied to the

device address pins A2, A1 and A0. Each of them is typically connected either to GND for

logic 0, or to VCC for logic 1. These pins represent the three LSB bits of the device 7-bit

address. The other four MSB bits of the address data are preset to ‘1001’ by hard wiring

inside the LM75B . Table 4 shows the device’s complete address and indicates that up to

8 devices can be connected to the same bus without address conflict. Because the input

pins, SCL, SDA and A2 to A0, are not internally biased, it is important that they should not

be left floating in any application.

 

Table 4.

Address table

1 = HIGH; 0 = LOW.

MSB

LSB

1

0

0

1

A2

A1

A0

 

 

7.4 Register list

 

The LM75B contains four data registers beside the pointer register as listed in Ta ble

5. The pointer value, read/write capability and default content at power-up of the

registers are also shown in Table 5.

 

Table 5.

Register table

Register

name

Pointer

value

R/W

POR

state

Description

Conf

01h

R/W

00h

Configuration register: contains a single 8-bit data

byte; to set the device operating condition; default = 0.

Temp

00h

read only

n/a

Temperature register: contains two 8-bit data bytes;

to store the measured Temp data.

Tos

03h

R/W

5000h

Over temperature shutdown threshold register:

contains two 8-bit data bytes; to store the over

temperature shutdown Tth(ots) limit;

default = 80

C.

Thyst

02h

R/W

4B00h

Hysteresis register: contains two 8-bit data bytes;

to store the hysteresis Thys limit; default = 75 C.

 

www.umw-ic.com

6

友台半导体有限公司

 

 

UMW

LM75B